The use of sleep EEG recordings is a routine procedure in the diagnostic work up of patients with suspected epilepsy. With respect to the diagnostic significance of paroxysmal EEG phenomena it is of importance to he informed about the incidence of such paroxysms in EEG's of healthy subjects. Several benign paroxysmal EEG phenomena during drowsiness or sleep have been identified (benign epileptiform transients of sleep (BETS), 14 and 6 positive spikes). Recent studies have shown that other, apparently aspecific, paroxysmal sharp transients may be recorded during drowsiness or sleep iii healthy subjects. In order to obtain more data on such paroxysmal EEG phenomena during sleep, a qualitative and semi quantitative analysis was performed on full night sleep recordings from 60 carefully selected healthy volunteers. Only 4 recordings were completely without the studied phenomena, all others showed some suspicious paroxysmal transients and some rare yet true specific epileptiform discharges were recorded in 8 subjects (13%), predominantly during transient periods of light non-REM sleep in the first two sleep cycles. The presence ol some sharp transients dining drowsiness or light sleep thus should be considered as a non-specific and non-pathological finding. Moreover these findings indicate the limited diagnostic specificity of the presence of a feu: epileptiform discharges during sleep, especially in patients with an ambiguous clinical history of epilepsy. (C) 1998 Elsevier Science Ireland Ltd.
